1. Field of the Invention
This invention relates to a holographic recording material and a method for holographic recording by the use of the material.
2. Prior Art Statement
A "hologram" is a photosensitive material on which an interference pattern formed using coherent light such as laser light has recorded. The holograms are now used for the formation of three-dimensional images and as optical elements. The characteristics which the holographic recording material is required to possess include, for example, sensitivity to laser beams such as of He-Ne (wavelength 633 nm), Ar (wavelength 515 and 488 nm), and He-Cd (wavelength 442 nm), high efficiency of holographic diffraction, high resolution, simplicity of developing treatment. Among the photosensitive materials in practical use, there are known plates of dichromic acid gelatin and bleached dry plates of silver salts of the type used as ordinary photographic materials. These materials have been reported by Masato Nakashima and Kazuo Hanano in "Display Hologram Handbook", pages 66 and 67, Gyoin Shokan (1985) and Terutsugu Ose, Hiroyoshi Saito, Shunichi Tanaka, Jumpei Tsujiuchi, and Takeshi Namioka in "Optical Engineering Handbook", pages 351 to 353, Asakura Shoten (1986), for example.
The conventional photosensitive materials, however, have a disadvantage in that the manufacture of a hologram entails complicated treatments and the holograms made of such materials require a wet developing treatment, though silver salts possess high sensitivity and dichromate gelatin possesses high diffraction efficiency. As means of overcoming this problem, a method using a photopolymerization type recording material formed mainly of two kinds of monomer mixtures has been proposed [W. J. Tomlinson et al, "Appl. Opt. Vol. 15, 534 (1976)]. This method effects holographic recording in the recording material by photopolymerizing the recording material falling in the part of an interference pattern high in luminous energy thereby causing modulation in refractive index in that part. The recording material falling in the part of the interference pattern low in luminous energy, however, remains as unreacted monomer. The pattern recorded on the recording material, if any, must therefore, be stabilized by having the entire surface of the recording material exposed to ultraviolet light, for example. Besides, this recording material is disadvantageous in that it is deficient in such practical properties as sensitivity to laser beam, diffraction efficiency, and resolution.
In the circumstances, there is a strong need to develop a holographic recording material excelling in sensitivity to laser beam, diffraction efficiency, and resolution as well as a method for holographic recording.